1. Field of the Invention
The present invention relates generally to recording and reading data from magnetic storage media and, more particularly, to an improved magnetic write head design for writing timing-based servo patterns on flexible magnetic storage media.
2. Description of the Related Art
Servo control systems that maintain the position of a magnetic head relative to tracks in magnetic storage media are well known. European Patent Application EP 0 690 442 A2, published Jan. 3, 1995, entitled xe2x80x9cServo Control Systemxe2x80x9d, Albrecht et al., describes a servo control system having a magnetic recording head for writing servo position code across the width of the magnetic recording tape and down the length of the tape. The head also has multiple gaps in the down-the-tape direction. The head can write a pattern along the length of the tape wherein the pattern contains multiple gaps spaced across the width of the tape. The advantage of such a recording head is the ability to write servo code along the entire length of the tape in discrete areas (bands) across the entire width of the tape in a single pass. This increases position accuracy of one pattern with respect to another. This also provides a huge economic advantage because writing each band separately would be significantly more expensive.
As shown in section in FIG. 1, a typical prior art head 100 is fabricated from two parallel pieces of ferrite 110 separated by a layer of glass 120. The top surface of the ferrite-glass-ferrite head 100 is curved, defining the contact surface of the tape. This curved surface is covered first with a thin magnetic seed layer 140 and then later with a layer 130 of magnetic material several microns thick. Gaps 150 defining the writing pattern extend through the magnetic layer 130 to the seed layer 140 over the central glass region. A wire winding 160 with one or more turns passes through a groove 170 in the ferrite extending across the long axis of the head 100 next to the glass. Current passing through the wire 160 energizes magnetic fields in the gaps 150. The magnetic field writes the gap pattern on the passing tape (not shown). Contact between the passing tape and the head causes wear to both the tape and the head thereby decreasing the life of both.
Using the prior art approach, each head 100 must be fabricated individually (i.e., discretely). The small size and shape of the discrete heads makes it difficult to apply a photoresist layer that has a uniform thickness. Forming a uniform photoresist layer is an especially important consideration because the photoresist is used to pattern the recording gaps. Photoresist thickness non-uniformity directly and adversely affects the quality of the patterns, especially for narrow gap dimensions. Such patterns require the formation of narrow lines (on the order of 1.5 xcexcm). The potential for decreased linewidth will permit a more efficient write and more precise position signal, improving servo control. Also, because the surface is curved, one must compensate for the curvature of the head in the photolithographic process. It is particularly difficult to apply an even layer of photoresist to pattern the recording gaps on this curved surface. Applying resist by spinning is difficult in the case where the length-to-width ratio of a part is far greater than unity. Although resist can be electroplated, dipped or sprayed onto the part, these methods are cumbersome and have not been refined for submicron geometric tolerances.
To produce this rounded shape, the heads must be individually machined although they could be produced in bar form to reduce fabrication costs. FIG. 2 illustrates a bar 200 containing several heads 100. Lines 210 perpendicular to the long axis indicate where the bars could be sawed apart to form individual heads 100. Although the bars 200 can be cut up into several heads 100, the procedure is still not very efficient and provides identical or even more difficult challenges to achieving photoresist uniformity.
Thus, it can be seen that multiple gap servo write heads cause wear to the heads and to the tape, are expensive to manufacture, have limited servo pattern definition, and hinder the use of magnetic storage devices in many applications.
Therefore, an unresolved need exists for a batch fabrication technique that will increase the manufacturing efficiency of servo write heads and also improve servo pattern definition for fine features while reducing tape and head wear.
A batch fabrication technique is described that increases the manufacturing efficiency of servo write heads and also improves servo pattern definition for fine features, while reducing tape and head wear. Multiple heads are fabricated as a batch from one or more ferrite wafers. A nominally flat, large wafer surface and a contour suitable for uniform photoresist application and planar photolithography permit fine servo pattern definition. A rounded leading edge on the head creates an air bearing to reduce wear of the tape and of the head. Moreover, any head wear occurs at the leading edge rather than in the region of the head where the servo pattern is formed.
According to one aspect of the invention, the servo write head has a substantially planar head surface. A leading edge is disposed adjacent to the head surface such that the tape contacts the leading edge before passing over the head surface. In a preferred embodiment, the leading edge is rounded to form an air bearing between the head surface and the tape. A rounded trailing edge may be disposed adjacent to the head surface such that the tape passes over the trailing edge after passing over the head surface. Either of the leading or trailing edges may be rounded through blending, grinding or faceting from the head surface.
The head can advantageously permit single pass recording of servo data over the width and length of the tape. A head as described will experience reduced wear of the magnetic recording region of the head. In a preferred embodiment, the geometry of the head will cause low contact pressure on tape at the edges of head so that any wear occurring at edges of the head will be reduced and head life will be extended.
According to another aspect of the invention, the head is formed from an upper ferrite wafer having a non-magnetic spacer. Non-magnetic material is photolithographically defined to produce gaps above the spacer. The non-magnetic material may be photoresist, semiconductor materials, glass, metal or the like. The material may even be removed later to leave air gaps. The non-magnetic material forms a region where the field loops out to intersect the passing tape, thereby transferring a magnetic pattern to tape. The defined gap pattern may differ from the pattern written to tape. By appropriate choice of gap pattern, the servo pattern may be enhanced. An additional non-magnetic space can be formed in the back of the upper ferrite wafer proximate to the spacer to enhance the magnetic circuit. Additionally, a lower ferrite wafer may be mated to the upper ferrite wafer to complete a magnetic circuit around the gaps. An inductive winding may pass through a channel in the ferrite or spacer. Multiple heads may be formed through batch processing of the upper and lower ferrite wafers.
Furthermore, the design of the head is such that the head can be readily made through batch fabrication. Moreover, the head will permit fabrication with increased process control as well as increased general dimensional control. The potential for decreased linewidth will permit a more efficient write and more precise position signal, improving servo control. The write efficiency is further enhanced through completion of a magnetic circuit around the gaps.